There are signs and wonders in the heavens, although they may not always be what you first think. There is an old story of a Roman Emperor — Nero if I am not wrong — while lounging in his villa south of Rome — saw the northern sky awash with swirling red lights. Thinking that the City was afire, he sent his men to help put out the flames. But as it turned out, what he saw was the Aurora Borealis.
It might not be so dramatic as Nero thought, but events thousands of miles away can affect our weather and our view of the sky. Spaceweather.com has just issued an alert for “volcanic sunsets”, the various colorations of the sky, especially around the setting sun, due to gas and ashes erupted from the Kasatochi volcano in Alaska’s Aleutian islands.
The particles are of the right size to scatter sunlight of certain wavelengths, effectively acting as a filter to change the Sun’s apparently “monochromatic” light into a wide variety of hues. I put “monochromatic”, meaning one color, in quotation marks because our view of sunlight as white is merely an ironic illusion. While the sun’s light normally appears to us as a warm white, maybe slightly yellow, it’s light is really a mixture of all the colors of a rainbow. In fact a rainbow is sunlight spread out into all the constituent colors.
However, dust, molecules of water, smoke and a wide variety of airborne particles — aerosols such as the dust and sulfur dioxide in the volcanic eruptions — can result in a multicolored sunset.
We are accustomed to the golden and red hues of sunset, the painted sunset skies that are common from my home in Denver, which are caused by dust and larger molecules in the air. But in relatively small concentrations, smoke can turn the sky a milky blue or brownish, and other particles such as are frequently found in volcanic eruptions can cause less common and often dramatic pinks and purples and other unsuspected tints.
Don’t confuse these atmospheric effects (if you are so privileged as to observe them) with other unusual sky colorations caused by notilucent clouds, the aurorae, or even the faint hazy glow of the zodiacal lights.
The specific eruption that has caused the sunset light shows recently was several weeks ago, and presumably its affects will taper off over the next few days or weeks, so be sure to enjoy the sunsets soon. Of course it could happen again at any time, and sunsets can be spectacular at any time. If you are lucky, you’ll see something rare and unforgettable. But even if you aren’t lucky you can enjoy the sunset anyway. It’s never a waste of time.
“When in evening, ye say, it will be fair weather: For the sky is red. And in the morning, it will be foul weather today; for the sky is red and lowering.” Matthew XVI: 2-3
I have to admit it. The photo above is not a volcanic sunset, bur rather an “ordinary” winter sunset as seen from Denver in December 2007. And I may have used it before, but hey, it’s my photo!
Larry Sessions has written many favorite posts in EarthSky's Tonight area. He's a former planetarium director in Little Rock, Fort Worth and Denver and an adjunct faculty member at Metropolitan State University of Denver. He's a longtime member of NASA's Solar System Ambassadors program. His articles have appeared in numerous publications including Space.com, Sky & Telescope, Astronomy and Rolling Stone. His small book on world star lore, Constellations, was published by Running Press.